1. Field of the Invention
The present invention relates to a common zoom optical system almost commonly used as a component in a plurality of zoom lenses suitable for a video camera, digital still camera and the like using a solid-state image pick-up device and the like.
2. Related Background Art
Generally, a zoom lens has a merit in that a user can take a photograph with high degree of freedom while choosing a focal length at random (a state of a focal length of a lens being the shortest is a wide-angle end state and a state of a focal length of a lens being the longest is a telephoto end state.) Thus, in recent years, the zoom lens has been typically mounted on a camera photographing a subject using the solid-state image pick-up device such as CCD, MOS, etc., for example, the digital still camera, the video camera and the like. And in conjunction with this, a camera has been popular that increases a value dividing a focal length in a telephoto end state by a focal length in a wide-angle end state, namely, a zoom ratio and secures the long focal length in the telephoto end state and today such the camera has been broadly accepted by users, and many cameras with various specifications have been marketed.
Generally, in the digital still camera, the video camera and the like, a plurality of zoom lenses having different specifications for each product series has been developed. However, in order to develop a plurality of zoom lenses for each product series, much burden becomes necessary with respect to R&D manpower, development length and cost for expanding production facilities like production lines.
Then, in order to beef up the product series, by employing one optical system in another zoom lens as a common lens component, it becomes possible to develop a plurality of zoom lenses for each product series, too. But, these zoom lenses become similar in specifications such as the focal length, an f-number, the zoom ratio and the like, thereby resulting in increase in a camera having the similar specifications.
With such the background, a zoom lens has been known that is configured to include, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having positive refractive power and a fifth lens group having positive refractive power, and only change a screen size without changing angle of view by removing the fifth lens group (e.g., see Japanese Patent Application Laid-open No. 2003-121738.)
Also, a zoom lens has been known that is configured to include a taking lens and a changing lens group, and change the screen size without changing angle of view by placing the changing lens group on the optical path of the taking lens (e.g., see Japanese Patent Application Laid-open No. H07-199067.)
However, there are drawbacks in that fluctuation in aberrations and deviation in a position of an image plane can arise respectively upon zooming, by removing the fifth lens group in the zoom lens disclosed in Japanese Patent Application Laid-open No. 2003-121738 or placing the changing lens group in the zoom lens disclosed in Japanese Patent Application Laid-open No. H07-199067.